Impact of butanol-sunflower oil biodiesel–diesel blends on engine performance, combustion, and after-treatment emissions (DOC + SCR)

This study investigates the effects of n-butanol–sunflower biodiesel–diesel ternary blends on the combustion, performance, and emission characteristics of a single-cylinder compression ignition (CI) engine equipped with an integrated diesel oxidation catalyst and selective catalytic reduction (DOC + SCR) aftertreatment system. Eight fuel formulations were evaluated at 1800 rpm under four engine loads (10.98, 16.48, 21.97, and 27.46 Nm).: neat diesel (D100); binary n-butanol–diesel blends containing 5, 10, and 15 vol% butanol (D95BUT5, D90BUT10, and D85BUT15); a sunflower biodiesel–diesel blend containing 30 vol% biodiesel (B30D70); and ternary blends combining B30 with 5, 10, and 15 vol% butanol (B30D65BUT5, B30D60BUT10, and B30D55BUT15). Combustion parameters were derived from 50-cycle ensemble-averaged pressure data, while emissions were quantified upstream (P 1 ) and downstream (P 3 ) of the aftertreatment system. Results showed that D90BUT10 achieved the lowest specific fuel consumption (241.01 g/kWh) and highest brake thermal efficiency (33.97%) at 21.97 Nm, corresponding to a 4.4 percentage point improvement over D100 at the same condition. D85BUT15 yielded the lowest HC emissions, reaching 54.77 ppm at 10.98 Nm, whereas B30D55BUT15 produced the lowest CO emissions (0.032 vol%) under low-load conditions. However, B30-based blends generated the highest NO x concentrations, with a peak value of 2109 ppm at 16.48 Nm. Following DOC + SCR treatment, CO emissions were completely eliminated for all oxygenated blends, HC emissions decreased by 10–35% depending on load and fuel composition, and NO x conversion efficiency ranged between 40 and 68%, with the highest conversion observed at 27.46 Nm. An anomalous deterioration in combustion and performance was identified for B30D60BUT10 at intermediate loads, attributed to the combined effects of biodiesel-induced atomization limitations and butanol-related ignition delay. Overall, the study provides a systematic characterization of sunflower biodiesel–n-butanol ternary blend interactions within an integrated DOC + SCR framework and highlights the non-linear coupling between oxygenated fuel composition and aftertreatment performance.